The studies proposed here focus on the function of KCNQ potassium channels in the sensory hair cells of the auditory and vestibular systems. Mutations in four of the five members of this newly discovered class of voltage-gated ion channels cause inherited human diseases. At least three of these proteins are expressed in the auditory and vestibular periphery: KCNQ1, 3 and 4. Mutations in two of them, KCNQ1 and 4, cause severe auditory dysfunction. Although the etiologies of these inherited conditions are not well understood, the profound sensory deficits imply an important role for KNCQ proteins in normal auditory function. This project has two main goals. This first goal is to correlate expression of KCNQ potassium channels with the normal physiology of auditory and vestibular hair cells. This will provide new insight into how mutations in the KCNQ gene family lead to pathological states. The second goal is to investigate the role of KCNQ channels in synaptic transmission in the vestibular periphery. Specifically, we will test the hypothesis that the type I hair cell afferent synapse utilizes a novel form of K+-dependent neurotransmission. To address these questions we have devised a common strategy. A mutation within the pore-forming region of these potassium channels acts in a dominant manner to block conduction. Using virus-mediated gene transfer we will express mutant KCNQ genes in cells of organotypic cultures from the mouse auditory and vestibular organs. Expression of mutant KCNQ genes in normal cells will suppress the activity of wildtype KCNQ subunits. To assay for disrupted function we will characterize the electrophysiological properties of infected cells, identified by coexpression of green fluorescent protein, and neighboring uninfected control cells. Thus, in a specific and controlled manner we will link a molecular identity with its physiologic correlate.